Fluoroelastomer, curable composition and cured rubber article

ABSTRACT

A noncrystalline fluoroelastomer which is a copolymer consisting essentially of vinylidene fluoride and a fluoromonomer represented by the general formula (1):
 
CH 2 ═CFR f   (1)
 
wherein R f  is a straight or branched fluoroalkyl group containing 1 to 12 carbon atoms, and has a vinylidene fluoride units/fluoromonomer units mol ratio of 78/22 to 22/78 and a glass transition temperature of not higher than 25° C.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application claims benefit under 35 U.S.C. §119(e) of U.S.Provisional Application No. 61/157,706 filed Mar. 5, 2009, and U.S.Provisional Application No. 61/292,557 filed Jan. 6, 2010, incorporatedherein by reference in its entirety.

TECHNICAL FIELD

The present invention relates to a novel fluoroelastomer and a curablecomposition comprising the same and, further, to a cured rubber article.

BACKGROUND ART

Owing to their excellent characteristics, in particular their goodthermal stability, chemical resistance and oil resistance, vinylidenefluoride (VdF)/hexafluoropropylene (HFP) copolymers,VdF/HFP/tetrafluoroethylene (TFE) copolymers and like fluoroelastomers(fluororubbers) produced by using VdF as an essential constituentmonomer are used as the materials of various parts or members in suchfields as the automobile, airplane and semiconductor industries wheresevere use conditions, such as exposures to high temperatures and/orvarious chemicals, are unavoidable.

Several other polymers comprising VdF as a constituent unit are alsoknown; thus, for example, Patent Documents 1 and 2 describe thatpolymers were obtained by copolymerizing VdF and2,3,3,3-tetrafluoropropene.

PRIOR ART DOCUMENTS Patent Documents

-   Patent Document 1: U.S. Pat. No. 2,970,988-   Patent Document 2: United States Patent Application Publication    2008/0153978

SUMMARY OF THE INVENTION Problems which the Invention is to Solve

However, Patent Documents 1 and 2 do not describe any noncrystallinefluoroelastomers.

It is an object of the present invention to provide a noncrystallinefluoroelastomer low in glass transition temperature and excellent inamine resistance.

Means for Solving the Problems

The present inventors found that polymers comprising vinylidene fluorideunits and fluoromonomer units derived from a compound represented by thegeneral formula (1):CH₂═CFR_(f)  (1)wherein R_(f) is a straight or branched fluoroalkyl group containing 1to 12 carbon atoms, in specific proportions occur as noncrystallineelastomers and further found that they are very low in glass transitiontemperature and excellent in amine resistance. Such findings have nowled to completion of the present invention.

Namely, the present invention is a noncrystalline fluoroelastomer whichis a copolymer consisting essentially of vinylidene fluoride and afluoromonomer represented by the general formula (1):CH₂═CFR_(f)  (1)wherein R_(f) is a straight or branched fluoroalkyl group containing 1to 12 carbon atoms, and has a vinylidene fluoride units/fluoromonomerunits mol ratio of 78/22 to 22/78 and a glass transition temperature ofnot higher than 25° C. (Hereinafter referred to as “firstfluoroelastomer”)

The vinylidene fluoride units/fluoromonomer units mol ratio of the firstfluoroelastomer is preferably 78/22 to 60/40.

The present invention is a noncrystalline fluoroelastomer which is acopolymer consisting essentially of vinylidene fluoride, a fluoromonomerrepresented by the general formula (1):CH₂═CFR_(f)  (1)wherein R_(f) is a straight or branched fluoroalkyl group containing 1to 12 carbon atoms, and another monomer copolymerizable with bothvinylidene fluoride and said fluoromonomer of formula (1), and has avinylidene fluoride units/fluoromonomer units mol ratio of 85/15 to20/80, contains the other monomer units in the amount of 1 to 50 molpercent of all the monomer units and has a glass transition temperatureof not higher than 25° C. (Hereinafter referred to as “secondfluoroelastomer”)

The vinylidene fluoride units/fluoromonomer units mol ratio of thesecond fluoroelastomer is preferably 85/15 to 50/50.

The fluoromonomer of the first or second fluoroelastomer is preferably2,3,3,3-tetrafluoropropene.

The present invention is a curable composition comprising the first orsecond fluoroelastomer and a curing agent. Hereinafter, the curablecomposition comprising the first fluoroelastomer and a curing agent isreferred to as “first curable composition”. Hereinafter, the curablecomposition comprising the second fluoroelastomer and a curing agent isreferred to as “second curable composition”.

The present invention is a cured rubber article obtained by curing thefirst or second curable composition.

The present invention is a noncrystalline fluoroelastomer which is acopolymer comprising vinylidene fluoride, a fluoromonomer represented bythe general formula (1):CH₂═CFR_(f)  (1)wherein R_(f) is a straight or branched fluoroalkyl group containing 1to 12 carbon atoms, and another monomer copolymerizable with bothvinylidene fluoride and said fluoromonomer of formula (1), and has avinylidene fluoride units/fluoromonomer units mol ratio of 85/15 to20/80, contains the other monomer units in the amount of 0 to 50 molpercent of all the monomer units, has a glass transition temperature ofnot higher than 25° C. and contains at least one iodine atom and/or atleast one bromine atom, the total content thereof being 0.001 to 10% byweight. (Hereinafter referred to as “third fluoroelastomer”)

The third fluoroelastomer of the present invention is preferably acopolymer consisting essentially of vinylidene fluoride and afluoromonomer represented by the general formula (1):CH₂═CFR_(f)  (1)wherein R_(f) is a straight or branched fluoroalkyl group containing 1to 12 carbon atoms, and has a vinylidene fluoride units/fluoromonomerunits mol ratio of 80/20 to 20/80.

The vinylidene fluoride units/fluoromonomer units mol ratio of the thirdfluoroelastomer is preferably 85/15 to 50/50 and the other monomer unitsamount to 1 to 50 mol percent of all the monomer units.

The fluoromonomer of the third fluoroelastomer is preferably2,3,3,3-tetrafluoropropene.

The present invention is a curable composition comprising the thirdfluoroelastomer and a curing agent. (Hereinafter referred to as “thirdcurable composition”)

The third curable composition preferably contains an organic peroxide asthe curing agent.

The present invention is a cured rubber article obtained by curing thethird curable composition.

Effects of the Invention

The fluoroelastomers of the invention have good rubber elasticity andare excellent in low-temperature resistance and amine resistance aswell. The fluoroelastomers of the invention are lower in glasstransition temperature (Tg) than vinylidene fluoride(VdF)/hexafluoropropylene (HFP) copolymers when the comparison is madeunder the condition that the molar content of the fluoromonomer offormula (1) is equal to the molar content of hexafluoropropylene.

BRIEF DESCRIPTION OF THE DRAWING

The drawing is a graphic representation of the glass transitiontemperatures versus the mol fractions of a fluoromonomer of formula (1)or HFP for the copolymers of VdF and the fluoromonomer of formula (1) asobtained in Examples 2 to 5 and for the VdF/HFP copolymers obtained inComparative Examples 5 to 8.

DESCRIPTION OF EMBODIMENTS

The first, second and third fluoroelastomers of the invention eachcomprises vinylidene fluoride units and units derived from afluoromonomer represented by the general formula (1):CH₂═CFR_(f)  (1)wherein R_(f) is a straight or branched fluoroalkyl group containing 1to 12 carbon atoms, in specific proportions and, therefore, they arenoncrystalline elastomers and show a very low glass transitiontemperature. They are excellent in curability as well and, further,those fluoroelastomers comprising units derived from a fluoromonomerrepresented by the above general formula (1) are hardlydehydrofluorination and are excellent in amine resistance.

In the present specification, the term “noncrystalline” means that themelting peak (ΔH) appearing in DSC measurement (programming rate 10°C./minute) has an area not larger than 2.0 J/g.

The first, second and third fluoroelastomers of the present inventioncan have a glass transition temperature not higher than 25° C., or nothigher than 0° C. or, further, not higher than −20° C. Thefluoroelastomers of the invention show such a very low glass transitiontemperature and therefore are excellent in low-temperature resistance.

The glass transition temperature referred to above can be determined,using a DSC curve obtained by heating 10 mg of each sample at aprogramming rate of 10° C./minute using a differential scanningcolorimeter (Mettler DSC 822e), as the temperature indicated by thepoint of intersection of an extension of the baseline in the vicinity ofthe second-order transition point on the DSC curve with the tangent tothe DSC curve at the point of inflection.

The first fluoroelastomer of the present invention is a copolymerconsisting essentially of vinylidene fluoride and a fluoromonomerrepresented by the formula (1), and has a vinylidene fluorideunits/fluoromonomer units mol ratio of 78/22 to 22/78.

The vinylidene fluoride units/fluoromonomer units mol ratio in the firstfluoroelastomer of the invention is preferably 78/22 to 60/40.

The second fluoroelastomer of the invention is a copolymer

consisting essentially of vinylidene fluoride a fluoromonomerrepresented by the formula (1) and another monomer copolymerizable bothvinylidene fluoride and said fluoromonomer of formula (1), and has avinylidene fluoride units/fluoromonomer units mol ratio of 85/15 to20/80, contains the other monomer units in the amount of 1 to 50 molpercent of all the monomer units.

The vinylidene fluoride units/fluoromonomer units mol ratio is 85/15 to50/50, more preferably 85/15 to 60/40.

The other monomer units in the second fluoroelastomer of the inventionpreferably amount to 1 to 40 mol percent relative to all the monomerunits.

In the first and second fluoroelastamers of the invention, thefluoromonomer represented by the formula (1) is preferably a monomerhaving a straight-chain fluoroalkyl group as R_(f), more preferably amonomer having a straight-chain perfluoroalkyl group as R_(f). The groupR_(f) preferably contains 1 to 6 carbon atoms.

The fluoromonomer represented by the above formula (1) includes, amongothers, CH₂═CFCF₃, CH₂═CFCF₂CF₃, CH₂═CFCF₂CF₂CF₃ and CH₂═CFCF₂CF₂CF₂CF₃and, among them, CH₂═CFCF₃, namely 2,3,3,3-tetrafluoropropene, ispreferred.

The other monomer is not particularly restricted but may be any monomercopolymerizable with vinylidene fluoride and the fluoromonomerrepresented by the formula (1) and may comprise one or more monomerspecies.

The other monomer preferably comprises at least one species selectedfrom the group consisting of tetrafluoroethylene [TFE],hexafluoropropylene, perfluoro(methyl vinyl ether), perfluoro(ethylvinyl ether), perfluoro(propyl vinyl ether), chlorotrifluoroethylene,trifluoroethylene, hexafluoroisobutene, vinyl fluoride, ethylene,propylene, alkyl vinyl ethers and cure site monomers and, morepreferably, it is TFE. In a preferred mode of embodiment, the othermonomer comprises TFE alone.

As the cure site monomers in the second fluoroelastomer of the presentinvention, there may be mentioned, for example, iodine- orbromine-containing monomers represented by the general formula:CX¹ ₂═CX¹—R_(f) ¹CHR¹X²wherein X¹ is a hydrogen atom, a fluorine atom or —CH₃, R_(f) ¹ is afluoroalkylene group, a perfluoroalkylene group, a fluoropolyoxyalkylenegroup or a perfluoropolyoxyalkylene group, R¹ is a hydrogen atom or —CH₃and X² is an iodine atom or a bromine atom, monomers represented by thegeneral formula:CF₂═CFO(CF(CF₃)CF₂O)_(m)(CF₂)_(n)—X³wherein m is an integer of 0 to 5, n is an integer of 1 to 3 and X³ is acyano group, a carboxyl group, an alkoxycarbonyl group, an iodine atomor a bromine atom, and monomers represented by the general formula:CH₂═CFCF₂O(CF(CF₃)CF₂O)_(m)(CF(CF₃))_(n)—X⁴wherein m is an integer of 0 to 5, n is an integer of 1 to 3 and X⁴ is acyano group, a carboxyl group, an alkoxycarbonyl group, an iodine atom,a bromine atom or —CH₂OH.

Preferred among them is at least one species selected from the groupconsisting of CF₂═CFOCF(CF₃)CF₂OCF₂CF₂CN, CF₂═CFOCF(CF₃)CF₂OCF₂CF₂COOH,CF₂═CFOCF(CF₃)CF₂OCF₂CF₂CH₂I, CH₂═CFCF₂OCF(CF₃)CF₂OCF(CF₃)CN,CH₂═CFCF₂OCF(CF₃)CF₂OCF(CF₃)COOH and CH₂═CFCF₂OCF(CF₃)CF₂OCF(CF₃)CH₂OH.

The third fluoroelastomer of the invention is a copolymer comprisingvinylidene fluoride, a fluoromonomer represented by the general formula(1):CH₂═CFR_(f)  (1)wherein R_(f) is a straight or branched fluoroalkyl group containing 1to 12 carbon atoms, and another monomer copolymerizable with bothvinylidene fluoride and said fluoromonomer of formula (1), and has avinylidene fluoride units/fluoromonomer units mol ratio of 85/15 to20/80, contains the other monomer units in the amount of 0 to 50 molpercent of all the monomer units, has a glass transition temperature ofnot higher than 25° C. and contains at least one iodine atom and/or atleast one bromine atom, the total content thereof being 0.001 to 10% byweight.

The third fluoroelastomer of the invention is preferably a copolymerconsisting essentially of vinylidene fluoride and a fluoromonomerrepresented by the general formula (1):CH₂═CFR_(f)  (1)wherein R_(f) is a straight or branched fluoroalkyl group containing 1to 12 carbon atoms, or a copolymer consisting essentially of vinylidenefluoride, a fluoromonomer represented by the formula (1):CH₂═CFR_(f)  (1)wherein R_(f) is a straight or branched fluoroalkyl group containing 1to 12 carbon atoms, and another monomer copolymerizable with vinylidenefluoride and the above-mentioned fluoromonomer. In this case, the thirdfluoroelastomer is a copolymer consisting essentially of vinylidenefluoride and a fluoromonomer represented by the general formula (1) or acopolymer consisting essentially of vinylidene fluoride, a fluoromonomerrepresented by the general formula (1) and above mentioned the othermonomer, but the third fluoroelastomer may be produced by using anreactive emulsifier at a level at which the effects of the presentinvention will not be lessened. Also, the third fluoroelastomer maycomprise iodine termination derived chain transfer agent.

The third fluoroelastomer of the invention is more preferably acopolymer consisting essentially of vinylidene fluoride and afluoromonomer represented by the general formula (1):CH₂═CFR_(f)  (1)wherein R_(f) is a straight or branched fluoroalkyl group containing 1to 12 carbon atoms, and has a vinylidene fluoride units/fluoromonomerunits mol ratio of 80/20 to 20/80.

The vinylidene fluoride units/fluoromonomer units mol ratio in the thirdfluoroelastomer of the invention is preferably 85/15 to 50/50, and theother monomer units amount to 1 to 50 mol percent of all the monomerunits.

In the third fluoroelastomer of the invention, the fluoromonomer ispreferably 2,3,3,3-tetrafluoropropene.

Each monomer unit content is the value determined by an NMR technique.

The third fluoroelastomer of the invention contains iodine atoms and/orbromine atoms, with the total content thereof being 0.001 to 10% byweight. The total content of iodine atoms and bromine atoms ispreferably 0.01 to 5% by weight, more preferably 0.1 to 5% by weight.The iodine content can be determined by admixing 5 mg of Na₂SO₃ with 12mg of the sample (fluoroelastomer), combusting the mixture in an oxygenatmosphere in a quartz combustion flask using an absorbing solutionprepared by dissolving 30 mg of a 1:1 (weight ratio) mixture of Na₂CO₃and K₂CO₃ in 20 ml of pure water, followed by 30 minutes of standing andfurther followed by quantitation using a Shimadzu model 20A ionchromatograph. The working curve can be prepared by using standard KIsolutions having an iodine ion content of 0.5 ppm or 1.0 ppm.

As for the binding sites of iodine and bromine atoms, each iodine orbromine atom may be bound to a terminus of the main chain or theterminus of a side chain of the fluoroelastomer; of course, both suchsites may each be occupied by an iodine or bromine atom. Each iodineterminus or bromine terminus serves as a curing point (curing site) togive a cured fluoroelastomer having a high cure density and, inaddition, facilitate peroxide curing.

The third fluoroelastomer of the invention can be produced by using aniodine- or bromine-containing monomer as the cure site monomers or byusing a bromine compound or an iodine compound as the polymerizationinitiator or chain transfer agent.

The fluoromonomer of formula (1) in the third fluoroelastomer of theinvention is preferably a monomer in which R_(f) is a straight-chainfluoroalkyl group, more preferably a monomer in which R_(f) is astraight-chain perfluoroalkyl group. The number of carbon atoms in R_(f)is preferably 1 to 6.

The fluoromonomer represented by the above formula (1) includes, amongothers, CH₂═CFCF₃, CH₂═CFCF₂CF₃, CH₂═CFCF₂CF₂CF₃ and CH₂═CFCF₂CF₂CF₂CF₃and, among them, CH₂═CFCF₃, namely 2,3,3,3-tetrafluoropropene, ispreferred.

In the third fluoroelastomer of the invention, the other monomer (Curesite monomers are excluded.) is not particularly restricted but may beany monomer copolymerizable with vinylidene fluoride and thefluoromonomer represented by the formula (1) and may comprise one ormore monomer species.

The other monomer preferably comprises at least one species selectedfrom the group consisting of tetrafluoroethylene [TFE],hexafluoropropylene, perfluoro(methyl vinyl ether), perfluoro(ethylvinyl ether), perfluoro(propyl vinyl ether), chlorotrifluoroethylene,trifluoroethylene, hexafluoroisobutene, vinyl fluoride, ethylene,propylene, alkyl vinyl ethers and cure site monomers and, morepreferably, it is TFE. In a preferred mode of embodiment, the othermonomer comprises TFE alone. The other monomer in the thirdfluoroelastomer of the invention amount to 0 to 50 mol percent, relativeto all the monomer units. In a preferred mode of embodiment, the othermonomer in the third fluoroelastomer of the invention amount to 1 to 50mol percent, relative to all the monomer units.

As the cure site monomers in the third fluoroelastomer of the invention,there may be mentioned, for example, iodine- or bromine-containingmonomers represented by the general formula:CX¹ ₂═CX¹—R_(f) ¹CHR¹X²wherein X¹ is a hydrogen atom, a fluorine atom or —CH₃, R_(f) ¹ is afluoroalkylene group, a perfluoroalkylene group, a fluoropolyoxyalkylenegroup or a perfluoropolyoxyalkylene group, R¹ is a hydrogen atom or —CH₃and X² is an iodine atom or a bromine atom, iodine- orbromine-containing monomers represented by the general formula:CX¹ ₂═CX¹—R_(f) ¹X²wherein X¹ is a hydrogen atom, a fluorine atom or —CH₃, R_(f) ¹ is afluoroalkylene group, a perfluoroalkylene group, a fluoropolyoxyalkylenegroup or a perfluoropolyoxyalkylene group, R¹ is a hydrogen atom or —CH₃and X² is an iodine atom or a bromine atom, preferably iodine-containingmonomers represented by the general formula:CH₂═CH(CF₂)_(n)Iwherein n is integer of 2 to 8, monomers represented by the generalformula:CF₂═CFO(CF(CF₃)CF₂O)_(m)(CF₂)_(n)—X³wherein m is an integer of 0 to 5, n is an integer of 1 to 3 and X³ is acyano group, a carboxyl group, an alkoxycarbonyl group, an iodine atomor a bromine atom, monomers represented by the general formula:CH₂═CFCF₂O(CF(CF₃)CF₂O)_(m)(CF(CF₃))_(n)—X⁴wherein m is an integer of 0 to 5, n is an integer of 1 to 3 and X⁴ is acyano group, a carboxyl group, an alkoxycarbonyl group, an iodine atom,a bromine atom or —CH₂OH, monomers represented by the general formula:R²R³═CR⁴—Z—CR⁵═CR⁶R⁷wherein R², R³, R⁴, R⁵, R⁶ and R⁷ are the same or different and eachrepresent a hydrogen atom or an alkyl group containing 1 to 5 carbonatoms, Z optionally having one or more oxygen atoms is a straight orbranched alkylene group containing 1 to 18 carbon atoms, a straight orbranched cycloalkylene group containing 3 to 18 carbon atoms, a straightor branched (per) fluoroalkylene group containing 1 to 10 carbon atoms,a straight or branched (per) fluoropolyoxyalkylene group containing 1 to10 carbon atoms or a straight or branched (per)fluoropolyoxyalkylenegroup represented by following formula:-(Q)_(p)-CF₂O—(CF₂CF₂O)_(n)(CF₂O)_(n)—CF₂-(Q)wherein each Q is the same or different and a alkylene group or anoxyalkylene group containing 1 to 10 carbon atoms, each p is the same ordifferent and O or 1, m and n are integer numbers and m/n is 0.2 to 5,molecular weight of the (per)fluoropolyoxyalkylene group is 500 to10000.

As the monomers represented by the general formula R²R³═CR⁴—Z—CR⁶═CR⁶R⁷,there may be mentioned, for example, CH₂═CH—(CF₂)₄—CH═CH₂,CH₂═CH—(CF₂)₆—CH═CH₂, monomer represented by a following formula:CH₂═CH—Z¹—CH═CH₂wherein Z¹ is fluoropolyoxyalkylene group represented by a formula—CH₂OCH₂—CF₂O—(CF₂CF₂O)_(m1)(CF₂O)_(n1)—CF₂—CH₂OCH₂—, m1/n1 is 0.5.Molecular weight of the monomer is 2000.

In a preferred mode of embodiment, the curing site-imparting monomercomprises at least one species selected from the group consisting ofCF₂═CFOCF(CF₃)CF₂OCF₂CF₂CN, CF₂═CFOCF(CF₃)CF₂OCF₂CF₂COOH,CF₂═CFOCF(CF₃)CF₂OCF₂CF₂CH₂I, CF₂═CFOCF₂CF₂CH₂I,CH₂═CFCF₂OCF(CF₃)CF₂OCF(CF₃)CN, CH₂═CFCF₂OCF(CF₃)CF₂OCF(CF₃)COOH,CH₂═CFCF₂OCF(CF₃)CF₂OCF(CF₃)CH₂OH and CH₂═CHCF₂CF₂I, CH₂═CH(CF₂)₂CH═CH₂.

In another preferred mode of embodiment, the curing site-impartingmonomer comprises at least one monomer selected from the groupconsisting, for example, of iodine- or bromine-containing monomersrepresented by the general formula:CX¹ ₂═CX¹—R_(f) ¹CHR¹X²wherein X¹ is a hydrogen atom, a fluorine atom or —CH₃, R_(f) ¹ is afluoroalkylene group, a perfluoroalkylene group, a fluoropolyoxyalkylenegroup or a perfluoropolyoxyalkylene group, R¹ is a hydrogen atom or —CH₃and X² is an iodine atom or a bromine atom, iodine- orbromine-containing monomers represented by the general formula:CX¹ ₂═CX¹—R_(f) ¹X²wherein X¹ is a hydrogen atom, a fluorine atom or —CH₃, R_(f) ¹ is afluoroalkylene group, a perfluoroalkylene group, a fluoropolyoxyalkylenegroup or a perfluoropolyoxyalkylene group, R¹ is a hydrogen atom or —CH₃and X² is an iodine atom or a bromine atom, preferably iodine-containingmonomers represented by the general formula:CH₂═CH(CF₂)_(n)Iwherein n is integer of 2 to 8, monomers represented by the generalformula:CF₂═CFO(CF(CF₃)CF₂O)_(m)(CF₂)_(n)—X⁵wherein m is an integer of 0 to 5, n is an integer of 1 to 3 and X⁵ isan iodine atom or a bromine atom, and monomers represented by thegeneral formula:CH₂═CFCF₂O(CF(CF₃)CF₂O)_(m)(CF(CF₃))_(n)—X⁵wherein m is an integer of 0 to 5, n is an integer of 1 to 3 and X⁵ isan iodine atom or a bromine atom. By using such an iodine- orbromine-containing monomer as the other monomer, it also becomespossible to produce the third fluoroelastomer of the invention.

The curing site-imparting monomer in the third fluoroelastomer of theinvention preferably amount to 0.01 to 10 mol percent, more preferably0.01 to 2 mol percent, relative to all the monomer units.

The first, second and third fluoroelastomers of the invention can beproduced by a conventional radical polymerization method. The manner ofpolymerization may be any of such manners as bulk polymerization,solution polymerization, suspension polymerization and emulsionpolymerization; emulsion polymerization is preferred, however, since itcan be easily carried out on an industrial scale.

In the above polymerization, a polymerization initiator, a chaintransfer agent, a surfactant and a solvent can be used, and these mayrespectively be ones known in the art.

In the production, by polymerization, of the first, second or thirdfluoroelastomer of the invention, an oil-soluble radical polymerizationinitiator or a water-soluble radical initiator can be used as thepolymerization initiator.

The oil-soluble radical polymerization initiator may be any of knownoil-soluble peroxides; typical examples are, for example, dialkylperoxydicarbonates such as diisopropyl peroxydicarbonate anddi-sec-butyl peroxydicarbonate, peroxyesters such as tert-butylperoxyisobutyrate and tert-butyl peroxypivalate, dialkyl peroxides suchas

-   di-tert-butyl peroxide and, further,-   di(ω-hydro-dodecafluoroheptanoyl)peroxide,-   di(ω-hydro-tetradecafluoroheptanoyl)peroxide,-   di(ω-hydro-hexadecafluorononanoyl)peroxide,-   di(perfluorobutyryl)peroxide, di(perfluorovaleryl)peroxide,-   di(perfluorohexanoyl)peroxide, di(perfluoroheptanoyl) peroxide,    di(perfluorooctanoyl)peroxide,-   di(perfluorononanoyl)peroxide,-   di(ω-chloro-hexafluorobutyryl)peroxide,-   di(ω-chloro-decafluorohexanoyl)peroxide,-   di(ω-chloro-tetradecafluorooctanoyl)peroxide,-   ω-hydro-dodecafluoroheptanoyl ω-hydrohexadecafluorononanoyl    peroxide, ω-chloro-hexafluorobutyryl-   ω-chloro-decafluorohexanoyl peroxide,-   ω-hydrododecafluoroheptanoyl perfluorobutyryl peroxide,-   di(dichloropentafluorobutanoyl)peroxide,-   di(trichlorooctafluorohexanoyl)peroxide,-   di(tetrachloroundecafluorooctanoyl)peroxide,-   di(pentachlorotetradecafluorodecanoyl)peroxide,-   di(undecachlorotriacontafluorodocosanoyl)peroxide and like-   di[perfluoro(or fluorochloro)acyl]peroxides.

The water-soluble radical polymerization initiator may be, for example,such a known water-soluble peroxide as the ammonium salt, potassium saltor sodium salt of persulfuric acid, perboric acid, perchloric acid,perphosphoric acid, percarbonic acid or the like, tert-butyl permaleateor tert-butyl hydroperoxide. It may also contain such a reducing agentas a sulfite or a sulfite salt in combination, and this may be used inan amount of 0.1 to 20 times the amount of the peroxide.

While the level of addition of the radical polymerization initiator isnot particularly restricted, the initiator may be added all at once atthe initial stage of polymerization or in portions or continuously in amanner such that the amount thereof added each time may not cause amarked reduction in rate of polymerization (for example, a concentrationof several ppm relative to water may be obtained). From the apparatusviewpoint, the upper limit thereto is within the range in which the heatof polymerization can be dissipated.

Usable as the surfactant are nonionic surfactants, anionic surfactantsand cationic surfactants, among others; preferred are straight orbranched fluorinated anionic surfactants containing 4 to 20 carbonatoms, for example ammonium perfluorooctanoate and the like. The levelof addition thereof is preferably 10 to 5000 ppm. (relative to theamount of water used in the polymerization). More preferably 50 to 5000ppm.

Also, Usable as the surfactant are reactive emulsifiers. The reactiveemulsifiers are not particularly restricted but may be any monomerhaving at least one unsaturated bond and at least one hydrophilic group;thus, mention may be made of CF₂═CFCF₂OCF(CF₃)CF₂OCF(CF₃)COONH₄, forinstance. The level of addition thereof is preferably 10 to 5000 ppm.(relative to the amount of water used in the polymerization). Morepreferably 50 to 5000 ppm.

A solvent incapable of inducing chain transfer is preferred as thesolvent. In the case of solution polymerization, mention may be made ofdichloropentafluoropropane (R-225) and, in the case of emulsionpolymerization or suspension polymerization, mention may be made ofwater or mixtures of water and a water-soluble organic solvent.

As the chain transfer agent to be used in the production of the first orsecond fluoroelastomers of the invention by polymerization, there may bementioned such esters as dimethyl malonate, diethyl malonate, methylacetate, ethyl acetate, butyl acetate and dimethyl succinate and,further, isopentane, methane, ethane, propane, isopropanol, acetone,various mercaptans, carbon tetrachloride and cyclohexane, among others.

A bromine compound or an iodine compound may also be used as the chaintransfer agent. As the method of carrying out the polymerization using abromine compound or an iodine compound, there may be mentioned themethod comprising carrying out emulsion polymerization in an aqueousmedium under pressure in the presence of a bromine compound or an iodinecompound in a substantially oxygen-free condition (iodine transferpolymerization method). Typical examples of the bromine compound oriodine compound to be used are, for example, compounds represented bythe general formula:R²I_(x)Br_(y)wherein x and y each is an integer of 0 to 2, with the provision thatthey satisfy the relation 1≦x+y≦2, and R² is a saturated or unsaturatedfluorohydrocarbon or chlorofluorohydrocarbon group containing 1 to 16carbon atoms or a hydrocarbon group containing 1 to 3 carbon atoms andmay contain an oxygen atom or atoms. The use of such a bromine compoundor iodine compound results in introduction of iodine or bromine atomsinto the product polymer, so that they may function as sites of curing.

As the iodine compound, there may be mentioned, for example,

-   1,3-diiodoperfluoropropane, 2-iodoperfluoropropane,-   1,3-diiodo-2-chloroperfluoropropane,-   1,4-diiodoperfluorobutane,-   1,5-diiodo-2,4-dichloroperfluoropentane,-   1,6-diiodoperfluorohexane, 1,8-diiodoperfluorooctane,-   1,12-diiodoperfluorododecane,-   1,16-diiodoperfluorohexadecane, diiodomethane,-   1,2-diiodoethane, 1,3-diiodo-n-propane, CF₂Br₂, BrCF₂CF₂Br,-   CF₃CFBrCF₂Br, CFClBr₂, BrCF₂CFClBr, CFBrClCFClBr, BrCF₂CF₂CF₂Br,-   BrCF₂CFBrOCF₃, 1-bromo-2-iodoperfluoroethane,-   1-bromo-3-iodoperfluoropropane,-   1-bromo-4-iodoperfluorobutane,-   2-bromo-3-iodoperfluorobutane,-   3-bromo-4-iodoperfluorobutene-1,-   2-bromo-4-iodoperfluorobutene-1, monoiodo- and-   monobromo-substituted benzenes, diiodo- and-   monobromo-substituted benzenes, and (2-iodoethyl)- and-   (2-bromoethyl)-substituted benzenes, among others; these compounds    may be used singly or in combination.

Among those mentioned above, 1,4-diiodoperfluorobutane,1,6-diiodoperfluorohexane and 2-iodoperfluoropropane are preferably usedin view of their reactivity in polymerization, reactivity in curing andready availability, among others.

In producing the third fluoroelastomer of the invention bypolymerization, a bromine compound or an iodine compound is preferablyused as the chain transfer agent. As the method of carrying out thepolymerization using a bromine compound or an iodine compound, there maybe mentioned the method comprising carrying out emulsion polymerizationin an aqueous medium under pressure in the presence of a brominecompound or an iodine compound in a substantially oxygen-free condition(iodine transfer polymerization method). Typical examples of the brominecompound or iodine compound to be used are, for example, compoundsrepresented by the general formula:R²I_(x)Br_(y)wherein x and y each is an integer of 0 to 2, with the provision thatthey satisfy the relation 1≦x+y≦2, and R² is a saturated or unsaturatedfluorohydrocarbon or chlorofluorohydrocarbon group containing 1 to 16carbon atoms or a hydrocarbon group containing 1 to 3 carbon atoms andmay contain an oxygen atom or atoms. The use of such a bromine compoundor iodine compound results in introduction of iodine or bromine atomsinto the product polymer, so that they may function as sites of curing.

As the iodine compound, there may be mentioned, for example,

-   1,3-diiodoperfluoropropane, 2-iodoperfluoropropane,-   1,3-diiodo-2-chloroperfluoropropane,-   1,4-diiodoperfluorobutane,-   1,5-diiodo-2,4-dichloroperfluoropentane,-   1,6-diiodoperfluorohexane, 1,8-diiodoperfluorooctane,-   1,12-diiodoperfluorododecane,-   1,16-diiodoperfluorohexadecane, diiodomethane,-   1,2-diiodoethane, 1,3-diiodo-n-propane, CF₂Br₂, BrCF₂CF₂Br,-   CF₃CFBrCF₂Br, CFClBr₂, BrCF₂CFClBr, CFBrClCFClBr, BrCF₂CF₂CF₂Br,-   BrCF₂CFBrOCF₃, 1-bromo-2-iodoperfluoroethane,-   1-bromo-3-iodoperfluoropropane,-   1-bromo-4-iodoperfluorobutane,-   2-bromo-3-iodoperfluorobutane,-   3-bromo-4-iodoperfluorobutene-1,-   2-bromo-4-iodoperfluorobutene-1, monoiodo- and-   monobromo-substituted benzenes, diiodo- and-   monobromo-substituted benzenes, and (2-iodoethyl)- and-   (2-bromoethyl)-substituted benzenes, among others; these compounds    may be used singly or in combination.

Among those mentioned above, 1,4-diiodoperfluorobutane,1,6-diiodoperfluorohexane and 2-iodoperfluoropropane are preferably usedin view of their reactivity in polymerization, reactivity in curing andready availability, among others.

Also usable as the chain transfer agent mentioned above in producing thethird fluoroelastomer of the invention by polymerization are, forexample, such esters as dimethyl malonate, diethyl malonate, methylacetate, ethyl acetate, butyl acetate and dimethyl succinate and,further, isopentane, methane, ethane, propane, isopropanol, acetone,various mercaptans, carbon tetrachloride and cyclohexane, among others.

In the polymerization for producing the first, second and thirdfluoroelastomers of the invention, the polymerization temperature,polymerization pressure and polymerization time may respectively be −15to 150° C., atmospheric pressure to 6.5 MPa, and 1 to 24 hours, althoughthey may vary depending on the solvent and/or polymerization initiatorspecies selected. In particular, when a fluorine atom-containing,oil-soluble radical polymerization initiator is used as thepolymerization initiator in solution polymerization, the polymerizationtemperature is preferably −15 to 50° C., more preferably 10 to 35° C.When a fluorine atom-containing, oil-soluble radical polymerizationinitiator is used in emulsion or suspension polymerization, thepolymerization temperature is preferably 30 to 95° C. When awater-soluble radical polymerization initiator is used as thepolymerization initiator, the polymerization temperature is preferably 0to 100° C., more preferably 10 to 95° C.

The first, second or third fluoroelastomer of the invention may occur inany form, for example in the form of an aqueous dispersion or powder.

In the case of emulsion polymerization, the fluoroelastomer in powderform can be obtained by causing the dispersion after polymerization tocoagulate, washing the coagulum with water and dehydrating and dryingthe same. The coagulation can be caused by addition of an inorganicsalt, such as aluminum sulfate, or an organic acid, by application of ashearing force, or by freezing the dispersion. In the case of suspensionpolymerization, it can be obtained by recovering the polymer from thedispersion after polymerization and drying the same. In the case ofsolution polymerization, it can be obtained by subjecting thefluoroelastomer-containing solution as such to drying or, alternatively,by purifying the polymer by dropwise addition of a poor solvent.

The first, second or third fluoroelastomer of the invention is alsosuited for use as a low-temperature resistant seal material and, forthat reason, among others, it preferably has a number average molecularweight (Mn) of 7000 to 500000 and a weight average molecular weight (Mw)of 10000 to 1000000, with the ratio Mw/Mn preferably being 1.3 to 4.0.

The above-mentioned number average molecular weight (Mn), weight averagemolecular weight (Mw) and ratio Mw/Mn values are respectively the valuesdetermined by the GPC method.

For showing good moldability/processability, the first, second or thirdfluoroelastomer of the invention preferably has a Mooney viscosity at100° C. (ML1+10(100° C.)) of not lower than 2, more preferably not lowerthan 5. Also from the viewpoint of good moldability/processability, theMooney viscosity is preferably not higher than 200, more preferably nothigher than 150, still more preferably not higher than 100. Each Mooneyviscosity value referred to above is the value determined in accordancewith ASTM D 1646 and JIS K 6300.

The present invention relates also to a curable composition excellent incurability which is characterized in that it comprises theabove-mentioned first, second or third fluoroelastomer of the inventionand a curing agent.

The level of addition of the curing agent is 0.01 to 10 parts by mass,preferably 0.1 to 5 parts by mass, per 100 parts by mass of thefluoroelastomer. When the level of the curing agent is lower than 0.01part by mass, the degree of curing is insufficient, so that theperformance characteristics of the fluoroelastomer articles tend to beimpaired while, at addition levels exceeding 10 parts by mass, the curedensity becomes excessively high, so that the curing time becomesprolonged; in addition, such levels tend to be also disadvantageous fromthe economical viewpoint.

The above-mentioned curing agent is not particularly restricted but maybe any of those curing agents which are generally used in polyaminecuring, polyol curing or peroxide curing; preferably, however, itcomprises at least one species selected from the group consisting ofpolyamine compounds, polyhydroxy compounds and organic peroxides.

As the polyamine compounds, there may be mentioned, for example,hexamethylenediamine carbamate,N,N′-dicinnamylidene-1,6-hexamethylenediamine and4,4′-bis(aminocyclohexyl)methane carbamate. Among these,N,N′-dicinnamylidene-1,6-hexamethylenediamine is preferred.

Preferably used as the polyhydroxy compound are polyhydroxy aromaticcompounds in view of their excellent thermal stability.

The above-mentioned polyhydroxy aromatic compounds are not particularlyrestricted but include, among others, 2,2-bis(4-hydroxyphenyl)propane(hereinafter referred to as “bisphenol A”),2,2-bis(4-hydroxyphenyl)perfluoropropane (hereinafter referred to as“bisphenol AF”), resorcinol, 1,3-dihydroxybenzene,1,7-dihydroxynaphthalene, 2,7-dihydroxynaphthalene,1,6-dihydroxynaphthalene, 4,4′-dihydroxydiphenyl,4,4′-dihydroxystilbene, 2,6-dihydroxyanthracene, hydroquinone, catechol,2,2-bis(4-hydroxyphenyl)butane (hereinafter referred to as “bisphenolB”), 4,4-bis(4-hydroxyphenyl)valeric acid,2,2-bis(4-hydroxyphenyl)tetrafluorodichloropropane,4,4′-dihydroxydiphenyl sulfone, 4,4′-dihydroxydiphenyl ketone,tri(4-hydroxyphenyl)methane, 3,3′,5,5′-tetrachlorobisphenol A and3,3′,5,5′-tetrabromobisphenol A. These polyhydroxy aromatic compoundseach may occur in the form of an alkali metal salt or alkaline earthmetal salt, for instance. In the case of copolymer coagulation using anacid, the use of such metal salts is preferably avoided.

In the case of the curing agent being a polyhydroxy compound, thecurable composition of the invention preferably contains a curingpromoter. The curing promoter accelerates the formation ofintramolecular double bonds due to the dehydrofluorination reaction ofthe fluoroelastomer main chain and the addition of the polyhydroxycompound to the resulting double bonds.

As the curing promoter, there may be mentioned onium compounds, and thecuring promoter preferably comprises at least one species selected fromthe group consisting of onium compounds, in particular such ammoniumcompounds as quaternary ammonium salts, such phosphonium compounds asquaternary phosphonium salts, oxonium compounds, sulfonium compounds,cyclic amines and monofunctional amine compounds, more preferably atleast one species selected from the group consisting of quaternaryammonium salts and quaternary phosphonium salts.

The quaternary ammonium salts are not particularly restricted butinclude, among others,

-   8-methyl-1,8-diazabicyclo[5.4.0]-7-undecenium chloride,-   8-methyl-1,8-diazabicyclo[5.4.0]-7-undecenium iodide,-   8-methyl-1,8-diazabicyclo[5.4.0]-7-undecenium hydroxide,-   8-methyl-1,8-diazabicyclo[5.4.0]-7-undecenium methylsulfate,-   8-ethyl-1,8-diazabicyclo[5.4.0]-7-undecenium bromide,-   8-propyl-1,8-diazabicyclo[5.4.0]-7-undecenium bromide,-   8-dodecyl-1,8-diazabicyclo[5.4.0]-7-undecenium chloride,-   8-dodecyl-1,8-diazabicyclo[5.4.0]-7-undecenium hydroxide,-   8-eicosyl-1,8-diazabicyclo[5.4.0]-7-undecenium chloride,-   8-tetracosyl-1,8-diazabicyclo[5.4.0]-7-undecenium chloride,-   8-benzyl-1,8-diazabicyclo[5.4.0]-7-undecenium chloride (hereinafter    referred to as “DBU-B”),-   8-benzyl-1,8-diazabicyclo[5.4.0]-7-undecenium hydroxide,-   8-phenethyl-1,8-diazabicyclo[5.4.0]-7-undecenium chloride and    8-(3-phenylpropyl)-1,8-diazabicyclo[5.4.0]-7-undecenium chloride.    Among these, DBU-B is preferred from the viewpoint that the curing    performance thereof and the physical characteristics of the articles    are excellent.

The quaternary phosphonium salts are not particularly restricted butinclude, among others, tetrabutylphosphonium chloride,benzyltriphenylphosphonium chloride (hereinafter referred to as“BTPPC”), benzyltrimethylphosphonium chloride, benzyltributylphosphoniumchloride, tributylallylphosphonium chloride,tributyl-2-methoxypropylphosphonium chloride andbenzylphenyl(dimethylamino)phosphonium chloride. Among these,benzyltriphenylphosphonium chloride (BTPPC) is preferred from theviewpoint that the curing performance thereof and the physicalcharacteristics of the articles are excellent.

Also usable as the curing promoter are solid solutions of quaternaryammonium salts or quaternary ammonium salts with bisphenol AF as well asthe chlorine-free curing promoters disclosed in Japanese KokaiPublication H11-147891.

The level of addition of the curing promoter is preferably 0.01 to 8parts by mass, more preferably 0.02 to 5 parts by mass, per 100 parts bymass of the fluoroelastomer. At curing promoter addition levels below0.01 part by mass, the curing of the fluoroelastomer will not proceed toa sufficient extent, hence the articles obtained tend to show reducedthermal stability and oil resistance. At levels exceeding 8 parts bymass, the moldability/processability of the curable composition tends tobe lowered.

As for the organic peroxides, use may be made of those organic peroxideswhich readily generate peroxy radicals in the presence of an acid or anoxidation/reduction system, for example

-   1,1-bis(tert-butylperoxy)-3,5,5-trimethylcyclohexane,-   2,5-dimethylhexane 2,5-dihydroperoxide, di-tert-butyl peroxide,    tert-butyl cumyl peroxide, dicumyl peroxide,-   α,α-bis(tert-butylperoxy)-p-diisopropylbenzene,-   2,5-dimethyl-2,5-di(tert-butylperoxy)hexane,-   2,5-dimethyl-2,5-di(tert-butylperoxy)hexyne-3, benzoyl peroxide,    tert-butylperoxybenzene, tert-butyl peroxymaleate, tert-butyl    peroxyisopropylcarbonate and tert-butyl peroxybenzoate. Among these,-   2,5-dimethyl-2,5-di(tert-butylperoxy)hexane and-   2,5-dimethyl-2,5-di(tert-butylperoxy)hexyne-3 are preferred.

When the curing agent is an organic peroxide, the curable composition ofthe invention preferably contains a curing aid. As the curing aid, theremay be mentioned, for example, triallyl cyanurate, triallyl isocyanurate(TAIC), triacrylformal, triallyl trimellitate,N,N′-m-phenylenebismaleimide, dipropargyl terephthalate, diallylphthalate, tetraallyl terephthalamide, triallyl phosphate, bismaleimide,fluorinated triallyl isocyanurate(1,3,5-tris(2,3,3-trifluoro-2-propenyl)-1,3,5-triazine-2,4,6-trione),tris(diallylamino)-s-triazine, triallyl phosphate,N,N-diallylacrylamide, 1,6-divinyldodecafluorohexane,hexallylphosphoramide, N,N,N′,N′-tetraallylphthalamide,N,N,N′,N′-tetraallylmalonamide, trivinyl isocyanurate,2,4,6-trivinylmethyltrisiloxane, tri(5-norbornene-2-methylene) cyanurateand triallyl phosphate. Among these, triallyl isocyanurate (TAIC) ispreferred from the viewpoint that the curing performance thereof and thephysical characteristics of the articles are excellent.

The level of addition of the curing aid is 0.01 to 10 parts by mass,preferably 0.1 to 5.0 parts by mass, per 100 parts by mass of thefluoroelastomer. At curing aid levels lower than 0.01 part by mass, thecuring time tends to become too long to be suited to practical use and,at levels exceeding 10 parts by mass, the curing time becomes too shortand, in addition, the articles tend to show decreases in permanentcompression set.

The curing is generally realized by baking at a temperature of 150 to300° C. for 1 minute to 24 hours, although the curing conditions may beproperly selected according to the curing agent species employed, amongothers. The curing can be realized at ordinary pressure or underincreased or reduced pressure and in air as well.

The method of curing is not particularly restricted but use may be madeof steam curing, compression molding or any other conventional method bywhich the curing reaction is initiated by heating; the radiation curingmethod under ordinary temperature and ordinary pressure may also beused.

A post-treatment step called post-curing may also be made after a firstcuring treatment (called press vulcanization).

The polyamine curing using a polyamine compound as the curing agent canbe carried out in the same manner as in the prior art. For example,mention may be made of the method comprising subjecting thefluoroelastomer of the invention and a curing agent, if necessarytogether with a curing promoter and further another or other appropriatecompatible additives, to roll milling, then placing the kneaded mass ina mold and applying pressure thereto for press curing, which is followedby post-curing. As for the press curing conditions, the temperature isgenerally selected within the range of 100 to 200° C., the time withinthe range of 5 to 120 minutes, and the pressure within the range ofabout 2 to 10 MPa and, as for the post-curing conditions, thetemperature is generally selected within the range of 150 to 300° C.,and the time within the range of about 30 minutes to 30 hours.

The polyol curing using a polyhydroxy compound as the curing agent canbe carried out in the same manner as in the prior art. For example,mention may be made of the method comprising subjecting thefluoroelastomer of the invention and a curing agent, if necessarytogether with a curing promoter and further another or other appropriatecompatible additives, to roll milling, then placing the kneaded mass ina mold and applying pressure thereto for press curing, which is followedby post-curing. For the kneading, an internal mixer, a Banbury mixer orthe like can be preferably used. Generally, the press curing can becarried out at 2 to 10 MPa and 100 to 200° C. for 5 to 60 minutes, andthe post-curing at 150 to 300° C. for 30 minutes to 30 hours.

The peroxide curing using an organic peroxide as the curing agent can becarried out in the same manner as in the prior art. For example, mentionmay be made of the method comprising subjecting the fluoroelastomer ofthe invention and a curing agent, if necessary together with a curingpromoter and further another or other appropriate compatible additives,to roll milling, then placing the kneaded mass in a mold and applyingpressure thereto for press curing, which is followed by post-curing.Generally, the press curing can be carried out at 2 to 10 MPa and 100 to200° C. for 5 to 60 minutes, and the post-curing at 150 to 300° C. for30 minutes to 30 hours.

The third curable composition of the invention, which contains the thirdfluoroelastomer containing at least one iodine atom and/or at least onebromine atom, the total content thereof being 0.001 to 10% by weight,can attain a further increased cure density since the iodine or brominetermini serve as curing points (curing sites).

The above-mentioned third curable composition of the invention morepreferably contains an organic peroxide as the curing agent. Since thethird fluoroelastomer mentioned above has iodine atoms and/or bromineatoms, with the total content thereof being 0.001 to 10% by weight, thepresence of an organic peroxide makes it possible to carry out theperoxide curing more easily. The organic peroxide includes thoseenumerated hereinabove and preferably comprises at least one compoundselected, among others, from among2,5-dimethyl-2,5-di(tert-butylperoxy)hexane and2,5-dimethyl-2,5-di(tert-butylperoxy)hexyne-3. Further, the thirdcurable composition of the invention preferably contains a curing aid.The curing aid includes those enumerated hereinabove and, among them,triallyl isocyanurate (TAIC) is preferred from the viewpoint that thecuring performance thereof and the physical characteristics of thearticles are excellent.

In the above-mentioned third curable composition, the level of additionof the curing aid is 0.01 to 10 parts by mass, preferably 0.1 to 5.0parts by mass, per 100 parts by mass of the fluoroelastomer. At curingaid levels lower than 0.01 part by mass, the curing time tends to becometoo long to be suited to practical use and, at levels exceeding 10 partsby mass, the curing time becomes too short and, in addition, thearticles tend to show decreases in permanent compression set.

The curing of the above-mentioned third curable composition is generallyrealized by baking at a temperature of 150 to 300° C. for 1 minute to 24hours, although the curing conditions may be properly selected accordingto the curing agent species employed, among others. The curing can berealized at ordinary pressure or under increased or reduced pressure andin air as well.

The above-mentioned third curable composition is preferably onecontaining an organic peroxide as the curing agent and capable of beingcured by peroxide curing. The peroxide curing using an organic peroxideas the curing agent can be carried out in the same manner as in theprior art. For example, mention may be made of the method comprisingsubjecting the third fluoroelastomer of the invention and a curingagent, if necessary together with a curing promoter and further anotheror other appropriate compatible additives, to roll milling, then placingthe kneaded mass in a mold and applying pressure thereto for presscuring, which is followed by post-curing. Generally, the press curingcan be carried out at 2 to 10 MPa and 100 to 200° C. for 5 to 60minutes, and the post-curing at 150 to 300° C. for 30 minutes to 30hours.

The first, second or third curable composition of the invention alsopreferably contains a filler. As the filler, there may be mentionedmetal oxides such as calcium oxide, titanium oxide and aluminum oxide;metal hydroxides such as magnesium hydroxide, aluminum hydroxide andcalcium hydroxide; carbonates such as magnesium carbonate, aluminumcarbonate, calcium carbonate and barium carbonate; silicates such asmagnesium silicate, calcium silicate, sodium silicate and aluminumsilicate; sulfates such as aluminum sulfate, calcium sulfate and bariumsulfate; synthetic hydrotalcite; metal sulfides such as molybdenumdisulfide, iron sulfide and copper sulfide; diatomaceous earth,asbestos, lithopone (zinc sulfide/barium sulfide), graphite, carbonblack, carbon fluoride, calcium fluoride, coke, finely pulverizedquartz, zinc white, talc, pulverized mica, wollastonite, carbon fibers,aramid fibers, various whiskers, glass fibers, organic reinforcingagents, organic fillers, polytetrafluoroethylene, mica, silica, Celite,clay and so forth.

The first, second or third curable composition of the invention alsopreferably contains a plasticizer. As the plasticizer, there may bementioned dioctyl phthalate and pentaerythritol, among others.

The first, second or third curable composition of the invention alsopreferably contains a processing aid. As the processing aid, there maybe mentioned higher fatty acids such as stearic acid, oleic acid, palmtic acid and lauric acid; higher fatty acid salts such as sodiumstearate and zinc stearate; higher fatty acid amides such as stearamideand oleamide; higher fatty acid esters such as ethyl oleate; higheraliphatic amines such as stearylamine and oleylamine; carnauba wax;petroleum waxes such as ceresin wax; polyglycols such as ethyleneglycol, glycerol and diethylene glycol; aliphatic hydrocarbons such aspetrolatum and paraffin; silicone oils, silicone polymers,low-molecular-weight polyethylene, phthalic acid esters, phosphoric acidesters, rosin, (halogenated) dialkylamines, surfactants, sulfonecompounds and fluorine-containing aids, among others.

The first, second or third curable composition of the invention maycontain one or more of acid acceptors, mold release agents, pigments,flame retardants, lubricants, light stabilizers, weathering stabilizers,antistatic agents, ultraviolet absorbers, antioxidants, blowing agents,perfumes, oils, softeners and so forth, each at an addition level atwhich the effects of the present invention will not be affected.

The first, second or third curable composition of the invention maycontain a solvent. When the fluoroelastomer is soluble in the solvent,the resulting composition can be used as a paint composition. Thesolvent includes ketone solvents and ester solvents, among others.

The first, second or third curable composition of the invention maycontain another polymer different from the fluoroelastomer of theinvention. As the other polymer, there may be mentioned, nitrilerubbers, acrylic rubbers, epichlorohydrin rubbers, fluorosiliconerubbers, silicone rubbers, fluorine-containing thermoplastic elastomersand poly(vinylidene fluoride), among others.

The first, second or third curable composition according to theinvention is preferably one obtained by kneading at least onefluoroelastomer according to the first, second or third aspect of theinvention together with a curing agent, if desired further together withone or more of the above-mentioned curing promoters and otheringredients.

The above kneading can be carried out using an open roll, Banbury mixer,press kneader or extruder, for instance; the use of a press kneader oran extruder such as a twin-screw extruder is preferred since a highshearing force can be applied therewith.

The present invention is also directed to cured rubber articles obtainedby curing the first, second or third curable composition of theinvention.

The cured rubber articles of the invention can be produced either bymolding the first, second or third curable composition and curing thethus-obtained articles or by carrying out the molding and curingsimultaneously. Further, the articles can also be obtained in the formof coating films by application of the curable composition, followed bycuring.

The method of molding is not particularly restricted but includes, amongothers, compression molding, extrusion molding, transfer molding andinjection molding.

The first, second or third cured rubber articles of the invention havegood thermal stability, oil resistance, amine resistance, chemicalresistance and low-temperature resistance and can be used as variousparts in the automobile, airplane and semiconductor industries. Owing totheir thermal stability, oil resistance and amine resistance, inparticular, they can be suitably used as parts or members for oilsealing, for example as hoses, oil seals and the like for automotiveengine oils. Other suitable articles are enumerated below.

Specifically, the articles include the following examples but are notlimited thereto.

Seal Members:

Mention may be made of O- (or square) rings, packing members, gaskets,diaphragms, other various seal members, etc., for use insemiconductor-related fields, e.g. in semiconductor productionequipment, liquid crystal panel production equipment, plasma panelproduction equipment, plasma address liquid crystal panels, fieldemission display panels and solar cell substrates, and these can be usedin CVD apparatus, dry etching apparatus, wet etching apparatus,oxidation/diffusion apparatus, sputtering apparatus, ashing apparatus,cleaning apparatus, ion implantation apparatus and exhausters. Morespecifically, they can be used as O-rings or sealing members for gatevalves, O-rings and other various seal members for quartz windows,O-rings and other various seal members for chambers, O-rings and othervarious seal members for gates, O-rings and other various seal membersfor bell jars, O-rings and other various seal members for couplings,O-rings, diaphragms and other various seal members for pumps, O-ringsand other various seal members for gas-controlling devices forsemiconductor production or processing, and O-rings and other variousseal members for resist developing solutions and detaching solutions.

In the automobile field, the articles can be used as gaskets, shaftseals, valve stem seals and various seal members for use in engines andperipheral equipment and as various seal members for automatictransmission (AT) units. As the seal members to be used in fuel systemsand peripheral devices, there may be mentioned O (square) rings, packingmembers, diaphragms and the like. More specifically, the articles can beused as engine head gaskets, metal gaskets, oil pan gaskets, crankshaftseals, cam shaft seals, valve stem seals, manifold packing members,seals for oxygen sensors, injector O-rings, injector packing members,fuel pump O-rings, diaphragms, crankshaft seals, gear box seals, powerpiston packing members, cylinder liner seals, valve stem seals,automatic transmission front pump seals, rear axle pinion seals,universal joint gaskets, speed meter pinion seals, foot brake pistoncups, torque transmission O-rings, oil seals, exhaust gas recirculationsystem seals, bearing seals, carburetor sensor diaphragms and the like.

In the airplane, rocket and shipbuilding fields, mention may be made ofdiaphragms, O (square) rings, valves, packing members, various sealmembers and the like, and these can be used in fuel systems. Morespecifically, the articles are used in the airplane field as jet enginevalve system seals, gaskets and O-rings, rotating shaft seals, hydraulicgaskets and fire wall seals, among others, and, in the shipbuildingfield, as screw propeller shaft stern seals, diesel engine suction andexhaust valve stem seals, butterfly valve seals, butterfly valve shaftseals and so forth.

In the chemical plant field, mention may be made of valves, packingmembers, diaphragms, O (square) rings, various seal members, amongothers, and these can be used in various steps of producing chemicalssuch as medicinal chemicals, agrochemicals, paints and resins. Morespecifically, the articles can be used as seals in chemical pumps,flowmeters and piping systems, heat exchanger seals, glass coolerpacking members in sulfuric acid production plants, seals inagrochemical spreaders and agrochemical transfer pumps, gas pipingseals, plating bath seals, high-temperature vacuum drier packingmembers, papermaking belt roller seals, fuel cell seals, wind tunneljoint seals, tube joining part packing members in gas chromatographs andpH meters, and seals, diaphragms and valve parts in analytical apparatusand physical and chemical apparatus, among others. In the oil drillingfield, the articles can be used as seal members such as a packer seal orseal members for logging for using at sea bottom or underground. Also,the articles can be used as seal members such as seal members for mudpump used for system of piping up oil above ground or at sea.

In the photographic field, including developing machines, in theprinting field, including printing machines and in the painting field,including painting equipment, the articles can be used as seals andvalve parts in dry-process copying machines, for instance.

In the food industry plant equipment field, mention may be made ofvalves, packing members, diaphragms, O (square) rings and various sealmembers, among others, and these can be used in foodproduction/processing steps. More specifically, the articles can be usedas plate type heat exchanger seals and vending machine electromagneticvalve seals, among others.

In the nuclear power plant equipment field, mention may be made ofpacking members, O-rings, diaphragms, valves and various seal members,among others.

In the general industry field, mention may be made of packing members,O-rings, diaphragms, valves and various seal members, among others. Morespecifically, the articles are used as seals and bearing seals inhydraulic and lubricating systems, windows and other seals in drycleaning equipment, uranium hexafluoride enrichment apparatus seals,seal (vacuum) valves in cyclotrons, automatic packaging machine seals,diaphragms in pumps (in pollution-monitoring apparatus) for analyzingsulfurous acid gas and chlorine gas in air, and so forth.

In the electric system field, the articles are specifically used asbullet train (Shinkansen) insulating oil caps, liquid-sealed transformerbenching seals and so forth.

In the fuel cell field, the articles are specifically used as sealmaterials between electrodes and separator and as seals in hydrogen,oxygen or product water piping systems, among others.

In the electronic component field, the articles are specifically used asradiator materials, electromagnetic wave shield materials, computer harddisk drive gaskets and so forth.

Those articles which can be produced by in situ molding are notparticularly restricted but include, among others, engine oil pangaskets, gaskets for magnetic recording apparatus, and clean room filterunit sealants.

They are also particularly suited for use as gaskets for magneticrecording apparatus (hard disk drives) and such sealants for cleanequipment as sealants in semiconductor manufacturing apparatus orstorehouses for wafers or other devices.

Further, they are particularly suited for use as packing members usedbetween fuel cell electrodes or in peripheral piping systems and asother sealants for fuel cells, among others.

Sliding Members:

In the automobile-related fields, mention may be made of piston rings,shaft seals, valve stem seals, crankshaft seals, cam shaft seals and oilseals, among others.

Generally, mention may be made of fluororubber products used as partssliding in contact with other materials.

Nonadhesive Members:

Mention may be made of hard disk crash stoppers in the computer field,for instance.

Fields Utilizing Water Repellency and Oil Repellency:

Mention may be made of automobile wiper blades, coated fabrics foroutdoor tents, and so forth.

EXAMPLES

The following examples illustrate the present invention morespecifically. These examples are, however, by no means limitative of thescope of the present invention.

The physical characteristics reported herein were measured by thefollowing methods.

[Copolymer Composition]

The copolymer compositions were determined by the NMR method.

-   Measuring apparatus: Varian VNMRS400-   Resonance frequency: 376.04 (Sfrq)-   Pulse wave: 30° (pw=6.8)    [Glass Transition Temperature (Tg)]

A DSC curve was obtained by heating 10 mg of a sample at a programmingrate of 10° C./minute using a differential scanning calorimeter (MettlerToredo DSC 822e), and the temperature indicated by the point ofintersection of an extension of the baseline in the vicinity of thesecond-order transition point on the DSC curve with the tangent to theDSC curve at the point of inflection was recorded as the glasstransition temperature of the sample.

[Heat of Fusion]

A DSC curve was obtained by heating 10 mg of a sample at a programmingrate of 10° C./minute using a differential scanning calorimeter (MettlerToredo DSC 822e), and the heat of fusion was calculated based on thesize of the fusion peak (ΔH) found on the DSC curve.

[Number Average Molecular Weight (Mn) and Weight Average MolecularWeight (Mw)]

Molecular weight calculations were made based on the results ofmeasurements by the GPC method using reference polystyrene species asstandards.

-   GPC apparatus: TOSOH HLC-8020-   Column: Shodex GPC806M (two columns), GPC801 and 802 each one column-   Developing solvent: tetrahydrofuran [THF]-   Sample concentration: 0.1% by mass-   Measurement temperature: 35° C.

Example 1

A 100-ml stainless steel (SUS) autoclave was charged with 40 ml ofdichloropentafluoropropane (R-225), the contents were cooled to the dryice temperature, 9.20 g of a perfluorohexane solution containingdi(2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptanoyl)peroxide at aconcentration of 8% by weight was quickly fed into the autoclave, thecontents were cooled to the dry ice temperature and, after nitrogensubstitution, 12.4 g of 2,3,3,3-tetrafluoropropene (hereinaftersometimes referred to as “1234yf” or merely as “yf”) and 7.1 g of VdFwere fed into the autoclave. The resulting mixture was shaken at 25° C.for 5.3 hours using a shaker. The colorless transparent solutionobtained was dried to give 2.5 g of a colorless transparent polymer. Thepolymer obtained was found to be composed of 1234yf and VdF in a molratio of 77/23. The Tg of the polymer obtained was determined to be24.6° C. by DSC. No melting peak was confirmed. The Mn was 7190 and theweight average molecular weight (Mw) was 10500, hence the ratio Mw/Mnwas 1.5.

Example 2

A 100-ml stainless steel (SUS) autoclave was charged with 40 ml ofdichloropentafluoropropane (R-225), the contents were cooled to the dryice temperature, 9.20 g of a perfluorohexane solution containingdi(2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptanoyl)peroxide at aconcentration of 8% by weight was quickly fed into the autoclave, thecontents were cooled to the dry ice temperature and, after nitrogensubstitution, 5.0 g of 2,3,3,3-tetrafluoropropene (hereinafter sometimesreferred to as “1234yf” or merely as “yf”) and 11.0 g of VdF were fedinto the autoclave. The resulting mixture was shaken at 25° C. for 5.2hours using a shaker. The colorless transparent solution obtained wasdried to give 3.5 g of a colorless transparent polymer. The polymerobtained was found to be composed of 1234yf and VdF in a mol ratio of51/49. The Tg of the polymer obtained was determined to be 7.0° C. byDSC. No melting peak was confirmed. The Mn was 10300 and the weightaverage molecular weight (Mw) was 16000, hence the ratio Mw/Mn was 1.5.

Example 3

A 100-ml stainless steel (SUS) autoclave was charged with 40 ml ofdichloropentafluoropropane (R-225), the contents were cooled to the dryice temperature, 9.20 g of a perfluorohexane solution containingdi(2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptanoyl)peroxide at aconcentration of 8% by weight was quickly fed into the autoclave, thecontents were cooled to the dry ice temperature and, after nitrogensubstitution, 2.7 g of 2,3,3,3-tetrafluoropropene (hereinafter sometimesreferred to as “1234yf” or merely as “yf”) and 12.6 g of VdF were fedinto the autoclave. The resulting mixture was shaken at 25° C. for 5.1hours using a shaker. The colorless transparent solution obtained wasdried to give 3.5 g of a colorless transparent polymer. The polymerobtained was found to be composed of 1234yf and VdF in a mol ratio of38/62. The Tg of the polymer obtained was determined to be −5.2° C. byDSC. No melting peak was confirmed. The Mn was 9200 and the weightaverage molecular weight (Mw) was 16000, hence the ratio Mw/Mn was 1.5.

Example 4

A 100-ml stainless steel (SUS) autoclave was charged with 40 ml ofdichloropentafluoropropane (R-225), the contents were cooled to the dryice temperature, 9.18 g of a perfluorohexane solution containingdi(2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptanoyl)peroxide at aconcentration of 8% by weight was quickly fed into the autoclave, thecontents were cooled to the dry ice temperature and, after nitrogensubstitution, 1.3 g of 2,3,3,3-tetrafluoropropene (hereinafter sometimesreferred to as “1234yf” or merely as “yf”) and 13.2 g of VdF were fedinto the autoclave. The resulting mixture was shaken at 25° C. for 1.2hours using a shaker. The colorless transparent solution obtained wasdried to give 0.9 g of a colorless transparent polymer. The polymerobtained was found to be composed of 1234yf and VdF in a mol ratio of28/72. The Tg of the polymer obtained was determined to be −16.6° C. byDSC. No melting peak was confirmed. The Mn was 7400 and the weightaverage molecular weight (Mw) was 12000, hence the ratio Mw/Mn was 1.7.

Example 5

A 100-ml stainless steel (SUS) autoclave was charged with 40 ml ofdichloropentafluoropropane (R-225), the contents were cooled to the dryice temperature, 2.35 g of a perfluorohexane solution containingdi(2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptanoyl)peroxide at aconcentration of 8% by weight was quickly fed into the autoclave, thecontents were cooled to the dry ice temperature and, after nitrogensubstitution, 0.8 g of 2,3,3,3-tetrafluoropropene (hereinafter sometimesreferred to as “1234yf” or merely as “yf”) and 13.4 g of VdF were fedinto the autoclave. The resulting mixture was shaken at 25° C. for 2.0hours using a shaker. The colorless transparent solution obtained wasdried to give 1.0 g of a colorless transparent polymer. The polymerobtained was found to be composed of 1234yf and VdF in a mol ratio of29/71. The Tg of the polymer obtained was determined to be −14.8° C. byDSC. No melting peak was confirmed. The Mn was 31000 and the weightaverage molecular weight (Mw) was 47000, hence the ratio Mw/Mn was 1.5.

Comparative Example 1

A 100-ml stainless steel (SUS) autoclave was charged with 40 ml ofdichloropentafluoropropane (R-225), the contents were cooled to the dryice temperature, 9.20 g of a perfluorohexane solution containingdi(2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptanoyl)peroxide at aconcentration of 8% by weight was quickly fed into the autoclave, thecontents were cooled to the dry ice temperature and, after nitrogensubstitution, 17.6 g of 2,3,3,3-tetrafluoropropene (hereinaftersometimes referred to as “1234yf” or merely as “yf”) and 4.0 g of VdFwere fed into the autoclave. The resulting mixture was shaken at 25° C.for 5.1 hours using a shaker. The colorless transparent solutionobtained was dried to give 2.8 g of a colorless transparent polymer. Thepolymer obtained was found to be composed of 1234yf and VdF in a molratio of 87/13. The Tg of the polymer obtained was determined to be32.4° C. by DSC. No melting peak was confirmed. The Mn was 7000 and theweight average molecular weight (Mw) was 10200, hence the ratio Mw/Mnwas 1.5.

Comparative Example 2

A 100-ml stainless steel (SUS) autoclave was charged with 40 ml ofdichloropentafluoropropane (R-225), the contents were cooled to the dryice temperature, 1.21 g of a perfluorohexane solution containingdi(2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptanoyl)peroxide at aconcentration of 8% by weight was quickly fed into the autoclave, thecontents were cooled to the dry ice temperature and, after nitrogensubstitution, 0.5 g of 2,3,3,3-tetrafluoropropene (hereinafter sometimesreferred to as “1234yf” or merely as “yf”) and 13.6 g of VdF were fedinto the autoclave. The resulting mixture was shaken at 25° C. for 1.6hours using a shaker. The colorless transparent solution obtained wasdried to give 2.1 g of a colorless transparent polymer. The polymerobtained was found to be composed of 1234yf and VdF in a mol ratio of4/96. Any Tg of the polymer obtained could not be confirmed. No meltingpeak was confirmed. The Mn was 14700 and the Mw was 25300, hence theratio Mw/Mn was 1.7.

Comparative Example 3

A 100-ml stainless steel (SUS) autoclave was charged with 40 ml ofdichloropentafluoropropane (R-225), the contents were cooled to the dryice temperature, 1.10 g of a perfluorohexane solution containingdi(2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptanoyl)peroxide at aconcentration of 8% by weight was quickly fed into the autoclave, thecontents were cooled to the dry ice temperature and, after nitrogensubstitution, 0.6 g of 2,3,3,3-tetrafluoropropene (hereinafter sometimesreferred to as “1234yf” or merely as “yf”) and 13.4 g of VdF were fedinto the autoclave. The resulting mixture was shaken at 25° C. for 1.0hour using a shaker. The colorless transparent solution obtained wasdried to give 0.3 g of a colorless transparent polymer. The polymerobtained was found to be composed of 1234yf and VdF in a mol ratio of13/87. The Tg of the polymer obtained was determined to be −23.5° C. byDSC. A melting peak showing a heat of fusion of 15 J/g was observed inthe vicinity of 96° C. The Mn was 13800 and the Mw was 26300, hence theratio Mw/Mn was 1.9.

Example 6

A 100-ml stainless steel (SUS) autoclave was charged with 40 ml ofdichloropentafluoropropane (R-225), the contents were cooled to the dryice temperature, 4.61 g of a perfluorohexane solution containingdi(2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptanoyl)peroxide at aconcentration of 8% by weight was quickly fed into the autoclave, thecontents were cooled to the dry ice temperature and, after nitrogensubstitution, 1.6 g of 2,3,3,3-tetrafluoropropene (hereinafter sometimesreferred to as “1234yf” or merely as “yf”), 3.7 g of TFE and 11.1 g ofVdF were fed into the autoclave. The resulting mixture was shaken at 25°C. for 3.0 hours using a shaker. The colorless transparent solutionobtained was dried to give 4.5 g of a colorless transparent polymer. Thepolymer obtained was found to be composed of 1234yf, VdF and TFE in amol ratio of 23/59/18. The Tg of the polymer obtained was determined tobe −11.3° C. by DSC. No melting peak was confirmed. The Mn was 58000 andthe weight average molecular weight (Mw) was 91000, hence the ratioMw/Mn was 1.6.

Example 7

A 100-ml stainless steel (SUS) autoclave was charged with 40 ml ofdichloropentafluoropropane (R-225), the contents were cooled to the dryice temperature, 1.25 g of a perfluorohexane solution containingdi(2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptanoyl)peroxide at aconcentration of 8% by weight was quickly fed into the autoclave, thecontents were cooled to the dry ice temperature and, after nitrogensubstitution, 1.0 g of 2,3,3,3-tetrafluoropropene (hereinafter sometimesreferred to as “1234yf” or merely as “yf”), 7.9 g of TFE and 8.0 g ofVdF were fed into the autoclave. The resulting mixture was shaken at 25°C. for 2.0 hours using a shaker. The colorless transparent solutionobtained was dried to give 1.6 g of a colorless transparent polymer. Thepolymer obtained was found to be composed of 1234yf, VdF and TFE in amol ratio of 21/55/24. The Tg of the polymer obtained was determined tobe −7.5° C. by DSC. A melting peak showing a heat of fusion of 1.6 J/gwas observed in the vicinity of 50° C. The Mn was 84000 and the weightaverage molecular weight (Mw) was 120000, hence the ratio Mw/Mn was 1.4.

Example 8

A 100-ml stainless steel (SUS) autoclave was charged with 40 ml ofdichloropentafluoropropane (R-225), the contents were cooled to the dryice temperature, 1.31 g of a perfluorohexane solution containingdi(2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptanoyl)peroxide at aconcentration of 8% by weight was quickly fed into the autoclave, thecontents were cooled to the dry ice temperature and, after nitrogensubstitution, 0.2 g of 2,3,3,3-tetrafluoropropene (hereinafter sometimesreferred to as “1234yf” or merely as “yf”), 1.0 g of TFE and 13.0 g ofVdF were fed into the autoclave. The resulting mixture was shaken at 25°C. for 3.0 hours using a shaker. The colorless transparent solutionobtained was dried to give 1.5 g of a colorless transparent polymer. Thepolymer obtained was found to be composed of 1234yf, VdF and TFE in amol ratio of 27/68/5. The Tg of the polymer obtained was determined tobe −12.3° C. by DSC. No melting peak was confirmed. The Mn was 29000 andthe weight average molecular weight (Mw) was 47000, hence the ratioMw/Mn was 1.6.

Example 9

A 100-ml stainless steel (SUS) autoclave was charged with 40 ml ofdichloropentafluoropropane (R-225), the contents were cooled to the dryice temperature, 1.21 g of a perfluorohexane solution containingdi(2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptanoyl)peroxide at aconcentration of 8% by weight was quickly fed into the autoclave, thecontents were cooled to the dry ice temperature and, after nitrogensubstitution, 1.0 g of 2,3,3,3-tetrafluoropropene (hereinafter sometimesreferred to as “1234yf” or merely as “yf”), 1.8 g of TFE and 12.0 g ofVdF were fed into the autoclave. The resulting mixture was shaken at 25°C. for 1.0 hours using a shaker. The colorless transparent solutionobtained was dried to give 0.6 g of a colorless transparent polymer. Thepolymer obtained was found to be composed of 1234yf, VdF and TFE in amol ratio of 17/70/13. The Tg of the polymer obtained was determined tobe −20.5° C. by DSC. No melting peak was confirmed. The Mn was 30000 andthe weight average molecular weight (Mw) was 49000, hence the ratioMw/Mn was 1.6.

Example 10

A 100-ml stainless steel (SUS) autoclave was charged with 40 ml ofdichloropentafluoropropane (R-225), the contents were cooled to the dryice temperature, 1.13 g of a perfluorohexane solution containingdi(2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptanoyl)peroxide at aconcentration of 8% by weight was quickly fed into the autoclave, thecontents were cooled to the dry ice temperature and, after nitrogensubstitution, 3.4 g of 2,3,3,3-tetrafluoropropene (hereinafter sometimesreferred to as “1234yf” or merely as “yf”), 3.4 g of TFE and 9.7 g ofVdF were fed into the autoclave. The resulting mixture was shaken at 25°C. for 0.5 hours using a shaker. The colorless transparent solutionobtained was dried to give 0.2 g of a colorless transparent polymer. Thepolymer obtained was found to be composed of 1234yf, VdF and TFE in amol ratio of 39/50/11. The Tg of the polymer obtained was determined tobe 2.8° C. by DSC. No melting peak was confirmed. The Mn was 16800 andthe weight average molecular weight (Mw) was 31000, hence the ratioMw/Mn was 1.9.

Comparative Example 4

A 100-ml stainless steel (SUS) autoclave was charged with 40 ml ofdichloropentafluoropropane (R-225), the contents were cooled to the dryice temperature, 1.15 g of a perfluorohexane solution containingdi(2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptanoyl)peroxide at aconcentration of 8% by weight was quickly fed into the autoclave, thecontents were cooled to the dry ice temperature and, after nitrogensubstitution, 0.3 g of 2,3,3,3-tetrafluoropropene (hereinafter sometimesreferred to as “1234yf” or merely as “yf”), 4.0 g of TFE and 11.0 g ofVdF were fed into the autoclave. The resulting mixture was shaken at 25°C. for 1.0 hours using a shaker. The colorless transparent solutionobtained was dried to give 1.1 g of a colorless transparent polymer. Thepolymer obtained was found to be composed of 1234yf, VdF and TFE in amol ratio of 9/64/27. The Tg of the polymer obtained was determined tobe −15.9° C. by DSC. A melting peak showing a heat of fusion of 7.4 J/gwas observed in the vicinity of 92° C. The Mn was 26600 and the weightaverage molecular weight (Mw) was 57200, hence the ratio Mw/Mn was 2.2.

Comparative Example 5

A 100-ml stainless steel (SUS) autoclave was charged with 40 ml ofdichloropentafluoropropane (R-225), the contents were cooled to the dryice temperature, 1.39 g of a perfluorohexane solution containingdi(2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptanoyl)peroxide at aconcentration of 8% by weight was quickly fed into the autoclave, thecontents were cooled to the dry ice temperature and, after nitrogensubstitution, 23.0 g of hexafluoropropylene (hereinafter sometimesreferred to as “HFP”) and 4.0 g of VdF were fed into the autoclave. Theresulting mixture was shaken at 25° C. for 8.7 hours using a shaker. Thecolorless transparent solution obtained was dried to give 1.6 g of acolorless transparent polymer. The polymer obtained was found to becomposed of HFP and VdF in a mol ratio of 69/31. The Tg of the polymerobtained was determined to be −3.8° C. by DSC. No melting peak wasconfirmed. The Mn was 10900 and the weight average molecular weight (Mw)was 17000, hence the ratio Mw/Mn was 1.6.

Comparative Example 6

A 100-ml stainless steel (SUS) autoclave was charged with 40 ml ofdichloropentafluoropropane (R-225), the contents were cooled to the dryice temperature, 1.55 g of a perfluorohexane solution containingdi(2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptanoyl)peroxide at aconcentration of 8% by weight was quickly fed into the autoclave, thecontents were cooled to the dry ice temperature and, after nitrogensubstitution, 27.3 g of hexafluoropropylene (hereinafter sometimesreferred to as “HFP”) and 2.0 g of VdF were fed into the autoclave. Theresulting mixture was shaken at 25° C. for 6.5 hours using a shaker. Thecolorless transparent solution obtained was dried to give 1.1 g of acolorless transparent polymer. The polymer obtained was found to becomposed of HFP and VdF in a mol ratio of 68/32. The Tg of the polymerobtained was determined to be −3.0° C. by DSC. No melting peak wasconfirmed. The Mn was 7700 and the weight average molecular weight (Mw)was 12000, hence the ratio Mw/Mn was 1.6.

Comparative Example 7

A 100-ml stainless steel (SUS) autoclave was charged with 40 ml ofdichloropentafluoropropane (R-225), the contents were cooled to the dryice temperature, 1.54 g of a perfluorohexane solution containingdi(2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptanoyl)peroxide at aconcentration of 8% by weight was quickly fed into the autoclave, thecontents were cooled to the dry ice temperature and, after nitrogensubstitution, 30.1 g of HFP and 1.4 g of VdF were fed into theautoclave. The resulting mixture was shaken at 25° C. for 7.4 hoursusing a shaker. The colorless transparent solution obtained was dried togive 1.6 g of a colorless transparent polymer. The polymer obtained wasfound to be composed of HFP and VdF in a mol ratio of 68/32. The Tg ofthe polymer obtained was determined to be −1.7° C. by DSC. No meltingpeak was confirmed. The Mn was 9900 and the weight average molecularweight (Mw) was 1500, hence the ratio Mw/Mn was 1.5.

Comparative Example 8

A 100-ml stainless steel (SUS) autoclave was charged with 40 ml ofdichloropentafluoropropane (R-225), the contents were cooled to the dryice temperature, 1.49 g of a perfluorohexane solution containingdi(2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptanoyl)peroxide at aconcentration of 8% by weight was quickly fed into the autoclave, thecontents were cooled to the dry ice temperature and, after nitrogensubstitution, 18.5 g of HFP and 6.2 g of VdF were fed into theautoclave. The resulting mixture was shaken at 25° C. for 2.1 hoursusing a shaker. The colorless transparent solution obtained was dried togive 1.2 g of a colorless transparent polymer. The polymer obtained wasfound to be composed of HFP and VdF in a mol ratio of 76/24. The Tg ofthe polymer obtained was determined to be −13.6° C. by DSC. No meltingpeak was confirmed. The Mn was 12000 and the weight average molecularweight (Mw) was 21000, hence the ratio Mw/Mn was 1.7.

As shown in the drawing, the VdF/2,3,3,3-tetrafluoropropene copolymersobtained in Examples 2 to 5 were found to be lower in glass transitiontemperature than the VdF/HFP copolymers obtained in Comparative Examples5 to 8.

Reference Example 1

A 500-ml stainless steel autoclave was charged with 250 ml of pure waterand 1.55 g of ammonium perfluorooctanoate and, after nitrogensubstitution, the autoclave inside was slightly pressurized with 1234yf,and the temperature was adjusted to 80° C. with stirring at 600 rpm,followed by feeding with 1234yf under pressure until arrival of theinside pressure at 0.29 MPa, further followed by feeding with VdF untilarrival at 0.72 MPa. A solution of 0.1 g of ammonium persulfate in 4 mlof pure water was fed into the autoclave under nitrogen pressure. At 6.5hours after start of the reaction, the pressure showed a reduction by0.04 MPa, when the autoclave inside gas was released, and the remainingdispersion was cooled and recovered. The dispersion had a solid contentof 2.1% by weight. Nitric acid was added to this dispersion for causingcoagulation to give about 2 g of a copolymer. According to NMR data, themol ratio 1234yf/VdF was 50/50. This copolymer had a glass transitiontemperature of 0.1° C.

Example 11

A 3-liter stainless steel autoclave was charged with 1500 ml of purewater, 15.03 g of ammonium perfluorooctanoate and 1.4297 g of1,4-diiodoperfluorobutane and, after nitrogen substitution, theautoclave inside was slightly pressurized with 1234yf, and thetemperature was adjusted to 80° C. with stirring at 600 rpm, followed byfeeding with 1234yf until arrival of the inside pressure at 1.21 MPa,further followed by feeding with a liquid monomer mixture composed ofVdF and 1234yf in a mol ratio of 69/31 under pressure until arrival at1.47 MPa. A solution of 0.0243 g of ammonium persulfate in 4 ml of purewater was fed into the autoclave under nitrogen pressure. Each time thepressure lowered to 1.42 MPa, the pressure was raised to 1.47 MPa withthe consistent monomer mixture. By repeating this procedure, a total of222 g of the consistent monomer mixture was fed into the autoclave over6.68 hours. The autoclave inside gas was then discharged, the remainingcontents were cooled, and 1730.6 g of a dispersion was recovered. Duringthe polymerization, ammonium persulfate was supplemented in anappropriate manner. The dispersion had a solid content of 13.3% byweight (polymer amount 230.3 g). Nitric acid was added to the dispersionfor coagulation, and the subsequent drying gave 224.41 g of a polymer.The polymer obtained was composed of 1234yf and VdF in a mol ratio of31/69. The Tg of the polymer obtained as determined by DSC was −16.6° C.The heat of fusion peak was not observed in the second run. The numberaverage molecular weight (Mn) was 69837, the weight average molecularweight (Mw) was 169549, the ratio Mw/Mn was 2.4, and the fluorinecontent was 62.6% by weight. The iodine content was 0.23% by weight. Theiodine content can be measured by admixing 5 mg of Na₂SO₃ with 12 mg ofthe sample (polymer obtained), combusting the mixture in oxygen in aquartz flask using an absorbing solution prepared by dissolving 30 mg ofa 1:1 (weight ratio) mixture of Na₂CO₃ and K₂CO₃ in 20 ml of pure waterand, after 30 minutes of standing, subjecting the absorbing solution toassaying using a Shimadzu 20A ion chromatograph. Two standard KIsolutions containing 0.5 ppm and 1.0 ppm of the iodide ion,respectively, were used for drawing the working curve used for theassaying.

Using the polymer (yf polymer) obtained in Example 11, a curablecomposition (composition 1) was prepared according to the formulationshown below in Table 1. Comparative curable compositions (1 to 3) wereprepared according to the respective formations shown below in Table 1.

Each curable composition was prepared in the conventional manner byblending the corresponding raw rubber with the indicated amounts of theadditives using an 8-inch open roll.

TABLE 1 Curable Comparative Comparative Comparative compo- curable com-curable com- curable com- sition 1 position 1 position 2 position 3Polymer of 100 — — — Example 11 (phr) VdF/HFP — — 100 — copolymer (phr)VdF/HFP/TFE — — — 100 copolymer (phr) TFE/Pr — 100 — — copolymer (phr)MT Carbon (phr) 20 20 20 20 Taic (phr) 4 5 4 4 Perhexa 25B (phr) 1.5 —1.5 1.5 Perbutyl P (phr) — 2 — —

The materials shown in Table 1 are as follows.

-   VdF/HFP copolymer (VdF/HFP=78/22 mol percent)-   VdF/HFP/TFE copolymer (VdF/HFP/TFE=50/30/20 mol percent)-   TFE/Pr copolymer (TFE/Pr=55/45 mol percent)-   MT Carbon (trademark: Thermax N990, product of Cancarb Ltd.)-   Taic (trademark: TAIC, product of Nippon Kasei Chemical Co., Ltd.)-   Perhexa 25B (product of NOF Corporation)-   Perbutyl P (product of NOF Corporation)

In Table 2, there are shown the VdF content, fluorine content, iodinecontent, glass transition temperature (Tg) and Mooney viscosity(ML1+10(100° C.)) of each of the polymer of Example 11 and the VdF/HFPcopolymer, VdF/HFP/TFE copolymer and TFE/Pr copolymer. The Mooneyviscosity measurements were made under the following conditions.

<Mooney Viscosity>

Measurements are made according to ASTM D 1646 and JIS K 6300.

-   Measuring apparatus: Alpha Technologies model MV2000E-   Number of rotor revolutions: 2 rpm-   Measurement temperature: 100° C.

TABLE 2 Polymer of TFE/Pr VdF/HFP VdF/HFP/TFE Example 11 copolymercopolymer copolymer VdF content 69 — 78 50 (mol %) Fluorine content 6357 66 69 (mass %) Iodine content 0.36 0 0.21 0.15 (mass %) Tg (° C.) −16−3 −16 −8 ML1 + 10 (100° C.) 54 60 34 97

Using the curable compositions produced in the above manner, theircuring (crosslinking) characteristics were examined. As for the curingcharacteristics, the lowest torque (ML), highest torque (MH), inductiontime (T10) and optimum cure time (T90) were measured according to JIS K6300-2 using a type II curastometer (product of JSR Corporation). Theresults are shown below in Table 3.

TABLE 3 Curable Comparative curable Comparative curable Comparativecurable composition 1 composition 1 composition 2 composition 3 Pressmolding conditions 160° C. × 10 min 170° C. × 10 min 160° C. × 10 min160° C. × 10 min Heat treatment conditions 180° C. × 4 hour 200° C. × 4hour 180° C. × 4 hour 180° C. × 4 hour Measurement temperature 160 170160 160 ML (N)  0.5  1.0  0.2  4.9 MH (N)  27.4  19.6  30.9  44.6 t10(min)  0.8  0.7  0.8  1.1 t190 (min)  2.5  9.6  2.1  2.4

Then, the articles resulting from curing of the respective curablecompositions were subjected to amine resistance testing, followed by100% modulus (M100), tensile strength at break (Tb)_(r) tensileelongation at break (Eb) and hardness (Hs [Shore A]) measurements.Volume swells (ΔV) were also determined. The initial characteristicsprior to amine resistance testing are shown in Table 4. The respectivemeasurement conditions were as given below.

The volume swell ΔV is the volumetric increase (indicative of the degreeof swelling) after immersion of each test specimen under predeterminedconditions and is represented by the formula: ΔV=(V−V₀)/V₀×100, where V₀is the original volume of the test specimen and V is the volume aftertesting. The volume value is calculated from the weight in air and theweight in water.

100% Modulus (M100)

Measurements were made according to JIS K 6251.

Tensile Strength at Break (Tb)

Measurements were made according to JIS K 6251.

Tensile Elongation at Break (Eb)

Measurements were made according to JIS K 6251.

Shore Hardness (Shore A)

Measurements were made according to JIS K 6253 using a type A durometer(peak value and after 1 second).

Specific Gravity

Each specific gravity value was determined after density measurementaccording to JIS K 6253.

TABLE 4 Curable Comparative Comparative Comparative compo- curable com-curable com- curable com- sition 1 position 1 position 2 position 3 100%Modulus 1.9 2.9 2.0 2.5 (MPa) Tb (MPa) 20.9 13.9 23.2 22.3 Eb (%) 455325 410 365 Hs (Shore A, peak) 67 73 67 71 Specific gravity 1.72 1.591.80 1.87Amine Resistance Testing

Each articles resulting from curing of the respective curablecompositions was subjected to immersion testing using a Toyota standardoil (product of Toyota Motor Corporation, SJ Oil Toyota Genuine Oil SJ10W-30) at 175° C. for 185 hours.

For each articles resulting from curing of the respective curablecompositions after immersion testing, the 100% modulus, Tb, Eb, Hs(Shore A, peak) and volume swell (ΔV) were measured; the respectivechanges from the values before immersion are shown in Table 5 inpercentages.

TABLE 5 Curable Comparative Comparative Comparative compo- curable com-curable com- curable com- sition 1 position 1 position 2 position 3 Δ100% 5 −10 15 12 Modulus (%) Δ Tb (%) −5 −6 −77 −64 Δ Eb (%) 1 −8 −54−42 Δ Hs (Shore A, −4 −7 −3 −2 peak) (%) Δ V (%) 0 8 1 1

INDUSTRIAL APPLICABILITY

The fluoroelastomer according to the invention can be suitably utilizedin producing various parts or members for use in the automobile,airplane and semiconductor industries.

The invention claimed is:
 1. A noncrystalline fluoroelastomer which is acopolymer comprising vinylidene fluoride, a fluoromonomer represented bythe general formula (1):CH₂═CFR_(f)  (1) wherein R_(f) is a straight or branched fluoroalkylgroup containing 1 to 12 carbon atoms, and another monomercopolymerizable with both vinylidene fluoride and said fluoromonomer offormula (1), and has a vinylidene fluoride units/fluoromonomer units molratio of 85/15 to 20/80, contains the other monomer units in the amountof 0 to 50 mol percent of all the monomer units, has a glass transitiontemperature of not higher than 25° C. and contains at least one iodineatom and/or at least one bromine atom, the total content thereof being0.001 to 10% by weight.
 2. The fluoroelastomer according to claim 1,which is a copolymer consisting essentially of vinylidene fluoride and afluoromonomer represented by the general formula (1):CH₂═CFR_(f)  (1) wherein R_(f) is a straight or branched fluoroalkylgroup containing 1 to 12 carbon atoms, and has a vinylidene fluorideunits/fluoromonomer units mol=ratio of 80/20 to 20/80.
 3. Thefluoroelastomer according to claim 1, wherein the vinylidene fluorideunits/fluoromonomer units mol ratio is 85/15 to 50/50 and the othermonomer units amount to 1 to 50 mol percent of all the monomer units. 4.The fluoroelastomer according to claim 1, wherein the fluoromonomer is2,3,3,3-tetrafluoropropene.
 5. A curable composition comprising thefluoroelastomer according to claim 1, and a curing agent.
 6. The curablecomposition according to claim 5, which contains an organic peroxide asthe curing agent.
 7. A cured rubber article obtained by curing thecurable composition according to claim 5.